Left-wing government candidate Claudia Sheinbaum is set to become Mexico's first female president after her rivals conceded in an election marred by political violence.
"I would like to thank the millions of Mexican women and men who voted for us on this historic day," said Sheinbaum, as supporters gathered in Mexico City to celebrate with fireworks.
The 61-year-old led on 57.9% of the vote with around two-thirds of ballots counted, the national electoral institute said on Monday.
Her main rival Xóchitl Gálvez came in second with around 29%, the authority said, with Jorge Álvarez Máynez from the Citizens' Movement in third on 10.6%. Full results are expected on Wednesday.
Gálvez and Álvarez called Sheinbaum to congratulate her on her victory, the president-elect told the press. The former mayor of Mexico City is set to take office on October 1.
Incumbent Andrés Manuel López Obrador also congratulated Sheinbaum in a video message. "With all my affection and respect, I congratulate Claudia Sheinbaum. She will be the first female president of Mexico in the 200-year history of the republic," he said.
López Obrador, who could not run for a second six-year term under the country's constitution, had endorsed the 61-year-old Sheinbaum as his successor in the left-wing Morena party.
Earlier, the announcement of preliminary results had been postponed several times.
"They are lying as always," wrote Gálvez on X before the first results were released.
Gálvez, a businesswoman, computer engineer and former senator, was backed by the broad centrist opposition alliance Strength and Heart for Mexico, formed by the National Action Party (PAN), the Institutional Revolutionary Party (PRI) and the Party of the Democratic Revolution (PRD).
Alongside the presidency, Mexicans voted to fill all seats in the Chamber of Deputies and the Senate, as well as regional and municipal posts, making it an election day of historic proportions.
In total, more than 20,000 offices were up for grabs, including governorships in eight of the 31 federal states and in the capital district.
Election officials said Sheinbaum's Morena party was also ahead in parliamentary elections.
Almost 100 million citizens were entitled to vote in the world's most populous Spanish-speaking country.
The campaign period was overshadowed by political violence, with at least 34 candidates killed since September, according to data from the Integralia consultancy firm. Officials say criminal groups warring for influence in some regions were behind many of the attacks.
At least three people were killed in violent incidents at separate polling stations in the states of Puebla, México and in the outskirts of Monterrey on election day, according to media reports.
In the central state of Puebla, a polling station in the municipality of Tlapanalá was unable to open after the ballots had been stolen, according to the electoral authority.
Voting had to be interrupted due to violence in the town of Coyomeapan, while in the cities of Chicomuselo and Pantelhó in the southern state of Chiapas, the elections were completely suspended due to the violence of the drug cartels in the region.